The present invention relates to a process for regenerating a catalyst. The catalyst is suitable for use in producing normally gaseous, normally liquid and optionally solid hydrocarbons from synthesis gas generally provided from a hydrocarbonaceous feed, for example a Fischer-Tropsch process. The invention further relates to the regenerated catalyst and the use thereof in Fischer-Tropsch processes. The invention especially relates to a process for regenerating a fixed bed of Fischer-Tropsch catalyst particles in situ in a reactor tube.
The Fischer-Tropsch process can be used for the conversion of synthesis gas (from hydrocarbonaceous feed stocks) into liquid and/or solid hydrocarbons. Generally, the feed stock (e.g. natural gas, associated gas and/or coal-bed methane, heavy and/or residual oil fractions, coal, biomass) is converted in a first step into a mixture of hydrogen and carbon monoxide (this mixture is often referred to as synthesis gas or syngas). The synthesis gas is then fed into a reactor where it is converted in one or more steps over a suitable catalyst at elevated temperature and pressure into paraffinic compounds and water. The obtained paraffinic compounds range from methane to high molecular weight modules. The obtained high molecular weight modules can comprise up to 200 carbon atoms, or, under particular circumstances, even more carbon atoms.
Numerous types of reactor systems have been developed for carrying out the Fischer-Tropsch reaction. For example, Fischer-Tropsch reactor systems include fixed bed reactors, especially multi-tubular fixed bed reactors, fluidised bed reactors, such as entrained fluidised bed reactors and fixed fluidised bed reactors, and slurry bed reactors such as three-phase slurry bubble columns and ebulated bed reactors.
Catalysts used in the Fischer-Tropsch synthesis often comprise a carrier based support material and one or more metals from Group 8-10 of the Periodic Table, especially from the cobalt or iron groups, optionally in combination with one or more metal oxides and/or metals as promoters selected from zirconium, titanium, chromium, vanadium and manganese, especially manganese. Such catalysts are known in the art and have been described for example, in the specifications of WO 9700231A and U.S. Pat. No. 4,595,703.
One of the limitations of a Fischer-Tropsch process is that the activity of the catalyst will, due to a number of factors, decrease over time. A catalyst that shows a decreased activity after use in a Fischer-Tropsch process is sometimes referred to as deactivated catalyst, even though it usually still shows activity. Sometimes such a catalyst is referred to as a deteriorated catalyst. Sometimes it is possible to regenerate the catalyst. This may be performed, for example, with one or more oxidation and/or reduction steps.
Even when regenerated, the catalysts often show a much lower physical strength then freshly prepared catalysts. This is especially the case for fixed bed catalysts, such as pellets and extrudates larger than 1 mm. And in case the shape and/or size of a fixed bed catalyst was changed during Fischer-Tropsch process, for example the particles may have swollen, regeneration generally does not reverse that. This thus limits the possibilities of using the regenerated fixed bed catalyst particles in a Fischer-Tropsch reaction again.
It would be an advancement in the art to provide an improved process for regenerating a cobalt comprising Fischer-Tropsch catalyst, especially a process in which the catalyst is regenerated in situ in a fixed bed reactor. Regenerating is sometimes referred to as rejuvenating.